Metabolism and transcriptional analyses reveal the mechanism of sucrose affecting the floral transition in pak choi (Brassica rapa ssp. chinensis Makino)

The yield and quality of pak choi decrease due to premature bolting in production. The floral transition is an important turning point before bolting in plants. In this study, the sugar content was measured, and it was found that sucrose, glucose and fructose increased significantly in shoot apices but decreased significantly in leaves during the floral transition of pak choi. Exogenous sucrose had a significant effect on the floral transition and bolting than glucose, making the bolting time 14.80 days earlier and the bolting rate reaching 100 %. Determination of the activities of sucrose phosphate synthase, sucrose synthase, and sucrose invertase showed that all enzyme activities increased during the floral transition, but the increase in anabolism was than that in catabolism, indicating that the process of sucrose synthesis was significantly enhanced during the floral transition. Analyzing the transcriptome in shoot apices at different floral stages revealed that the expression of most genes encoding enzymes was consistent with enzyme activities. To analyze the presumable molecular network in which sucrose affects the floral transition, a total of 5376 differentially expressed genes were identified during the floral transition. Trend analysis revealed that profiles 0 and 7 were significantly enriched in sucrose metabolism. In addition, they were also significantly enriched in floral development, circadian rhythm and photoperiod, and plant hormone signal transduction, which suggests that sucrose may contribute to the floral transition by regulating these pathways. These results provide an important reference value for further study on the mechanism by which sugar regulates the floral transition and provide specific data for the in-depth identification of key sucrose -related genes affecting the floral transition of pak choi.